May be able to help you with this one as I've had the same problem since
getting my new Oudie 2 last Summer and it has driven me nuts but I've
recently solved the issue with help from Andrej.

Go to SettingsHardware and uncheck GPS forwarding(it's an LNav only
thing), and more importantly uncheck Use backup GPS.

My theory is that if you are using an external GPS input on Comm 4 as
Primary with Backup GPS checked, then every time the Oudie senses that the
Primary GPS is on the threshold of useability it switches to backup and
then it can't make it's mind up which to use and you end up with the
continuous and very annoying switching back and forth between the two -
there's a conflict in there somewhere.

Yes you lose the back up GPS feature but do you really need it? - my set up
has been rock solid for weeks now when before I had the problem EVERY
flight.

Garmin 2+/ LX Nav V7/ Oudie 2 at 4800 baud.

Pete